Add property-based test for byte-identical replay determinism

[joaquinbejar]

Overview

Add property-based test ensuring byte-identical replay determinism: given the same ordered input stream, the engine produces identical execution reports and market-data messages, including sequence numbers, reject codes, and prices. Use proptest to generate random order sequences.

Context

• Files: tests/unit/, src/orderbook/sequencer/
• Related issue: global engine_seq monotonic across streams
• Sequencer already supports journal + replay; this test validates round-trip correctness
• Invariant: replay(snapshot, journal) ≡ live(snapshot, orders)

Acceptance criteria

• cargo clippy --all-targets --all-features -- -D warnings clean
• cargo fmt --all --check clean
• cargo test --all-features clean (including property tests)
• cargo build --release clean
• Property test: prop_replay_determinism runs 50 cases, all pass
• Test emits one failure example (seed, sequence) on first fail for debugging
• Invariant check: no seq gaps, maker price == trade price
• snapshots_match oracle confirms snapshot + replayed journal match initial state

[joaquinbejar]

Duplicate of #57, tracked there.

[joaquinbejar]

Duplicate of #57 — already implemented by PR #78. Closing as not planned.